Automatic ignition system for flaring waste combustible gases

ABSTRACT

AN AUTOMATIC IGNITION SYSTEM FOR FLARING WASTE COMBUSTIBLE GASES BEING EXHAUSTED THROUGH A STACK, WHICH UTILIZES AN IGNITOR BURNER WHICH IS AUTOMATICALLY ENERGIZED WHEN GASES ARE PASSED TO THE STACK. A MAIN FLAME SCANNER, IGNITOR BURNER SCANNER, AND A TIMER ARE SO INTERRELATED THAT A SAFE, ECONOMICAL, AND EFFICIENT OPERATION IS PERFORMED.

BEST AVALABLE Y 06!. 10, 1972 FREY EI'AL 3,691,229

AUTOMATIC IGNITION SYSTEM FOR FLARING WASTE COMBUSTIBLE GASES FiledSept. 25, 1970 64 La o o e {9 45 hn 5 07 887 I INVENTOR. DONALD J FEEYWARREN P. OPP

ATTOZNEY United States Patent "ice 3,697,229 AUTOMATIC IGNITION SYSTEMFOR FLARING WASTE COMBUSTIBLE GASES Donald J. Frey, North Canton, andWarren P. Opp, Simsbury, Conn., assignors to Combustion Engineering,Inc., Windsor, Conn.

Filed Sept. 25, 1970, Ser. No. 75,542 Int. Cl. F23d 13/20; F2311 9/08US. Cl. 23-277 C 3 Claims ABSTRACT OF THE DISCLOSURE An automaticignition system for flaring waste combustible gases being exhaustedthrough a stack, which utilizes an ignitor burner which is automaticallyenergized when gases are passed to the stack. A main flame scanner,ignitor burner scanner, and a timer are so interrelated that a safe,economical, and efficient operation is performed.

BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION The ignition systemof the present invention has an ignitor burner positioned in the upperportion of a stack which is automatically energized upon passage ofwaste gases to the stack, and which is de-energized upon ignition of thecombustibles inthe waste gases. Flame scanners for both the ignitorburner and the main gas stream assure safe, efiicient operation.

BRIEF DESCRIPTION OF THE DRAWING The figure is a combined schematic anddiagrammatic representation of the improved ignition system.

DESCRIPTION OF THE PREFERRED EMBODIMENT Looking now to the figure,numeral :10 designates a duct through which waste gases containingcombustibles, such as blast furnace gas, is conveyed. When these gasesare not utilized, such as burning in a furnace, they are generallyexhausted through a stack, such as 12, to the atmosphere. In thearrangement illustrated when it is desired to exhaust the gas throughstack 12, a damper 14 is opened. Connected to the damper and rotatabletherewith is a switch 16 which closes its associated contacts when thedamper 14 is in its open position. This energizes the main flame scanner1-8 by completing a circuit through conductors 20 and 22 to power source24.

Upon energization of scanner 18, rod 26 is moved to the right, closingnormally open switch 28. Closure of switch 28 completes two circuits, ashereinbelow described. A timer 40 is energized through conductors 37 and38, and normally closed switch 74. Also, an ignitor burner flame scanner34 is simultaneously energized, through conductors 32 and 36.

Upon energization of timer 40, a valve 44 in the fuel line to theignitor burner 46 is opened, for example by a solenoid, by closure ofswitch 84 upon movement to the left. Closure of switch 84 completes acircuit to Patented Oct. 10, 1972 the solenoid of valve 44 throughconductors 50, 52 and 42, 43. Closure of switch 84 also energizes anignition source, such as spark plug 48 for the ignitor burner 46. Thiscircuit is completed through conductors 54, 56 and 42, 43. Air is beingsupplied to the ignitor burner 46 continuously by a fan, not shown.

Upon establishment of flame at the ignitor burner 46, the flame scanner34 will detect such flame, moving the associated switch 45' to itsclosed position. Closure of switch 45 energizes relay 72 throughconductors 76, 78, and 82. Relay 72 will then open normally closedswitch 74, de-energizing the timer 40.

The ignitor burner will then ignite the combustibles in the blastfurnace gas flowing up through the stack 12. When this flame is detectedby scanner 18, switch arm 26 moves to the left, opening switch 28 andclosing switch 30. Opening of switch 28 de-activates the ignitor burnerand the ignitor flame scanner. The closing of switch 30 completes acircuit to indicating light 66 through conductors 68 and 70, which letsthe operator known that the waste gas is being burned.

The above operation takes place if everything performs as it should. If,for some reason, the main flame scanner 18 fails to detect flame in themain gas stream flow, a different operation takes place. The switch 28will remain closed, and switch 30 remains open. ,The circuit for theignitor scanner 34 thus stays energized. Although the circuits for thesolenoid valve 44 and ignition spark 48 are tie-energized by opening ofswitch 74, and thus also switch 84, new circuits for solenoid valve 44and ignition spark plug 48 are completed through switch 45 andconductors 88, 89 and 90, 91. This will keep the ignitor burner inoperation continuously in the'event the main flame scanner 18 fails todetect a flame.

The above situation can occur either because the scanner 18 ismalfunctioning and needs repair or be-v cause the blast furnace gas doesnot in fact ignite. In any event, the operator will be made aware of thefact that something is amiss when bulb 66 fails to light up. Thus theignitor burner scanner 34 acts to override the main flame scanner 18 andkeep the system in operation even though no flame is detected by themain scanner 18. If at any later time scanner 18 does detect a flame,swith 28 will be opened and switch 30 closed, indicating to the operatorthat the trouble has been overcome.

An alternative operation takes place if the ignitor burner fails toignite after a predetermined period of time when it is initially placedin operation. If this happens the ignitor burner scanner 34 will notdetect flame and thus switch 45 remains open. This keeps relay 72de-energized, switch 74 remains closed and timer 40 continues to run.After timer 40 has run for its full length of time, which can be set for30 or 60 seconds, it moves the switch arm along with switches 84 and 86to the right and is latched in that position. This opens switch 84, andsince switch 45 attached to the ignitor scanner 34 is in its openposition, shuts off valve 44 and ignition spark plug 48. Thesimultaneous closing of switch 86 completes a circuit through conductors58, 60 and 42, 43 to alarm light 62 and motor drive 64 of the damper 14.Motor 64 will close valve 14, opening switch =16, thus stopping the flowof gas to the stack and deenergizing the entire control system. Light 62indicates this situation to the operator, so that appropriatemaintenance can be performed.

From the above it can be seen that an ignitor burner has been providedfor igniting the combustibles in waste gases at the top of a stack whichis highly reliable and efficient in operation. In normal operation assoon as a flame is established in the main gas stream, the ignitor isshut off. If for some reason the main flame scanner does not detect aflame but the ignitor burner is performing satisfactorily, the wastegases continue to be discharged to the atmosphere with theignitorjburner remaining in operation as insurance. In the event theignitor flame scanner does not detect flame at the ignitor burner withina predetermined period of time after it is energized, the flow of wastegases to the stack is stopped; and a signal device makes the operatoraware of the malfunction.-

What is claimed is:

1. In combination, a stack through which waste gas containingcombustibles is to be discharged to the atmosphere, duct meansconnectedto the bottom of the stack, damper means positioned in the ductmeans, said damper means having a first closed position which preventsflow of the waste gas to the stack and a second open positionwhichpermits flow of the waste gas to the stack, first flame detectormeans located adjacent the top of the stack for detecting the presenceor absence of flame in the main stream of waste gas, saidfirst flamedetector means being electrically associated with the damper means suchthat it is energized when the damper means is in its open position, anignitor burner located adjacent the top of the stack for igniting thecombustibles contained in the waste gas, second flame detector means fordetecting the presence or absence of flame in the ignitor burner, saidsecond flame detector means being electrically associated with the firstflame detector means such that it is energized when the first flamedetector means senses no flame, and is de-energized when the first flamedetector means senses a flame, said ignitor burner having spark ignitionmeans and fuel supply means, said second flame detector means beingelectrically associated with the ignitor burner such that when no flameexists in the ignitor burner the spark ignition means is energized andfuel is supplied thereto, and whena flame is detected by the flrst flamedetector means, the second flame detector is de-energized, thusde-ener-gizing the spark ignition means and shutting ofi the fuel supplyto the ignitor burner.

2. The combination set forth in claim 1, including timer meanselectrically associated with the ignitor burner which de-energizes thespark ignition means and shuts off the fuel to the ignitor burner aftera predetermined period of time after the second flame detector means isenergized, if no flame is detected by the first and second flamedetector means.

3. The combination set forth in claim 2, wherein the timer means iselectrically associated with the damper means such that it closes thedamper. means after a predetermined period of time after the secondflame detector means is energized, if no flame is detected by the firstand second flame detector means.

References Cited UNITED STATES PATENTS 2,306,073 12/1942 Metcalf 250-217F 2,656,008 10/1953 Engel 23277 C 3,447,880 6/1969 Potts et a1. 431 X1,473,716 11/ 1923 Willcox 431202 X 2,888,981 6/1959 Ripple 431202 XJAMES H. TAYMAN, ]R., Primary Examiner US. Cl. X.R.

23232 E, 2 C; 43l-5, 14, 60, 71, 45, 202, 51; 26615, 31; 8 R, 18 R;356-207; 2502l.7 F

